Christchurch earthquakes of 2010-11 | New Zealand | Britannica.com Lyttelton Christchurch earthquakes of 2010–11, also called Canterbury earthquakes, series of tremors that occurred within and near the city of Christchurch , New Zealand, and the Canterbury Plains region from early September 2010 to late December 2011. The severest of those events were the earthquake (magnitude from 7.0 to 7.1) that struck on September 4, 2010, and the large, destructive aftershock (magnitude 6.3) that occurred on February 22, 2011. Woman surveying the damage to her home near Christchurch, close to the epicentre of the earthquake … Greg Bowker—New Zealand Herald/AP The principal event, sometimes referred to as the Darfield earthquake, struck at 4:35 am on September 4, 2010. The earthquake’s epicentre was located some 25 miles (40 km) west of Christchurch near the town of Darfield, and the focus was located about 6 miles (10 km) beneath the surface.

It was caused by right-lateral movement along a previously unknown regional strike-slip fault in the western section of the Canterbury Plains. The fault, later named the Greendale Fault, appeared about 50 to 56 miles (80 to 90 km) southeast of the boundary between the Australian and Pacific tectonic plates, and part of the fault became visible at the surface because of the earthquake. Thousands of smaller aftershocks occurred in the months that followed. Map of the central part of New Zealand’s South Island depicting the intensity of shaking caused by … Encyclopædia Britannica, Inc. The severest aftershock occurred at 12:51 pm on February 22, 2011. In contrast to the main shock, this aftershock was generated by oblique thrust faulting (where one side of the fault is thrust upward over the other) along a different, undiscovered fault. Like the main shock, however, the February 22 aftershock stemmed from the deformation along regional plate boundaries where the Pacific and Indo-Australian tectonic plates push against one another.

The focus of this temblor was relatively shallow, however, occurring only 3 miles (5 km) beneath the surface of Heathcote Valley, a suburb of Christchurch located on the Banks Peninsula . The aftershock’s depth and close proximity to Christchurch contributed to substantial shaking, surface cracking, and liquefaction (the conversion of soil into a fluidlike mass) in the city and surrounding area. Rescue workers blocking access to a collapsed building in central Christchurch, New Zealand, after … Mark Mitchell—New Zealand Herald/AP Similar Topics Northridge earthquake of 1994 Two large tremors struck the Christchurch metropolitan area during the early afternoon on June 13, 2011. The epicentres of each of these events, which possessed moment magnitudes of 5.6 and 6.3, were located some 10 km (6 miles) east of Christchurch at depths of 9 km (5.6 miles) and 7 km (4.4 miles), respectively.

The June 13 events were located farther east of the known extent of the Greendale Fault, and they appeared to have been generated by strike-slip faulting rather than by thrust faulting associated with the February 22 event. As a result, some seismologists have downplayed any direct association between the June 13 events and those of the main shock and February 22 aftershock. Other seismologists, however, suggested that stresses built up by these earlier temblors likely contributed to those of June 13, as well as to a series of shallow marine tremors ranging from magnitude 4.0 to magnitude 6.0 that shook the Christchurch area on December 23, 2011. Buildings and roads across the Christchurch region, which had been weakened by the September event and its aftershocks, were severely damaged or destroyed in the February event. Christchurch’s city centre was hit particularly hard and was evacuated. Over the months that followed, it was established that more than 180 people had died in the quake; many of them had been killed outright as structures collapsed and debris fell in the streets, crushing cars and buses as well.

Britannica Stories Scientists Ponder Menopause in Killer Whales One of the worst incidents was the collapse of the Canterbury Television (CTV) building, in the city centre, which was razed almost entirely. An estimated 100 or more people had been in the building at the time of the quake. Although some were rescued on the day of the quake, the search for others was suspended because it was thought that the remaining victims could not have survived; further, it was feared that the building’s remains were too unstable to be safe for rescue workers. Efforts resumed the following day, however, after the building was secured. Both the Anglican and Roman Catholic cathedrals of Christchurch suffered serious damage. Church officials believed that the latter structure was beyond repair, and the spire of the Anglican cathedral collapsed. The iconic Anglican cathedral of Christchurch, N.Z., damaged by the earthquake that struck the city … Mark Mitchell—New Zealand Herald/AP Mountains and the Sea: Fact or Fiction? Other towns in the area around Christchurch were seriously affected, although fewer lives were lost. The port town of Lyttelton , near the epicentre of the earthquake, sustained widespread damage to buildings, wharves, and other infrastructure.

Bexley and other suburbs were flooded after water mains broke; after the waters receded, quake-damaged roads and homes remained covered with silt. Impromptu community efforts distributed food and helped dig out the property of affected residents. Continuing aftershocks in the days after February 22 further weakened structures throughout the area, and portions of several suburbs had to be evacuated. The day after the quake, Prime Minister John Key declared a state of national emergency in the quake area, expanding his government’s powers to coordinate rescue and recovery efforts. More than 1,000 New Zealand Defence Force personnel led the response, aided by more than 100 members of the Singaporean armed forces who were in New Zealand for a joint training exercise at the time of the quake. Australia, Japan, Singapore, the United Kingdom, the United States, and other countries also sent hundreds of search-and-rescue workers. Rescue efforts were at times hampered, however, by the potential dangers posed by the aftershocks. Connect with Britannica Facebook Twitter YouTube Instagram Pinterest The removal of wreckage and official damage assessments were ongoing.

Hundreds of buildings in the central business district and some 10,000 dwellings were deemed to be unsalvageable, and it was expected that they would have to be demolished. Further, it was predicted that because the quake had rendered the land so unstable in some places, certain areas might have to be abandoned altogether. Indeed, it was believed that by the time of the June 13 aftershocks, some 50,000 former residents of Christchurch had already moved permanently to other places in New Zealand or to Australia. In March 2012 it was announced that because of additional damage it had sustained in the aftershocks, the Anglican cathedral was beyond repair and would be demolished.

Failures - 2010 Canterbury, New Zealand Earthquake 2010 Canterbury, New Zealand Earthquake 2010 Canterbury, New Zealand Earthquake (September 3, 2010) Matthew Vandersall, BAE/MAE, Penn State, 2011 Table of Contents Bibliography Introduction On September 4th, 2010 at 4:35 AM local time, a 7.1 magnitude earthquake affected the region of Canterbury, New Zealand. Reports indicate that the epicenter of the earthquake was 25 miles west of Christchurch near the town of Darfield. The initial quake lasted approximately 40 seconds with aftershocks continuing to be felt weeks after the event. New Zealand’s modern earthquake codes and policies helped to reduce major structural damage to infrastructure and life supporting facilities. Two people were reported to have been injured during the earthquake, one from a chimney collapse and another from shattered glass. Total damages were reported throughout the area to have caused a estimated $3 billion in repairs (EERI, 2010). Keywords: Canterbury, New Zealand, earthquake, seismic, liquefaction Figure 1: epicenter and intensity of earthquake.

Source: USGS. Earthquake Overview The hypocenter of the quake was approximately 40 km west of Christchurch at a depth of 10 km. The main shockwave was caused by a strike-slip or sliding motion along an East-West running fault. Further analysis showed that there was also a strong reverse or compressional faulting component to the main shock. The main fault was located on a flat agricultural area called the Canterbury Plains (Tonkin & Taylor, 2010). Figure 1 shows the location of the epicenter and intensity experienced by the surrounding region. Within the following two weeks, approximately 550 aftershocks were detected with a magnitude of at least 3.0. The strongest aftershock had occured shortly after the main event recording a magnitude of 5.6. There was no reported loss of life and only two people were injured during the event. The main contribution to the lack of injuries were that most people were asleep at the time of the earthquake (EERI, 2010). The geology of the region is comprised of alluvial or river borne deposits of sand, silt, and gravel from the surrounding rivers.

During a seismic event, loose soils such as sand, silt, and gravel are compacted causing the ground to settle. The groundwater table is located about two meters below the surface which affects the top 10 to 20 meters of sediments. As these smaller types of soil collapse, the groundwater between the particles will start to pressurize. The increase of water pressure is the cause of liquefaction as sand and silt are forced through the surface. Liquefaction will continue to occur until the pore water pressure has equalized. An additional consquence is the uplifting of underground utilities such as manholes (Tonkin & Taylor, 2010). Liquefaction and lateral spreading caused underground pipelines to break, disrupting access to drinkable water to many areas. Approximately 100 km of pipelines were in need of replacement in those areas affected by lateral spreading. A major concern was that sand and other debris was entering the pipelines and pumping stations, delaying access to restored service. It is estimated that 11,000 tons of sand was removed from both the pipes and the pumping stations (EERI, 2010).

As a result, the ground water table increased due to earthquake pressure, causing manholes to be uplifted. Building Performances Under the modern earthquake codes, recently engineered structures performed well. Within the last 15 years, the New Zealand government has made a push to improve these building codes. A number of older buildings which were constructed using reinforced concrete moment frames experienced minor structural damage. Steel structures are less common in the Christchurch area but generally performed as expected. The building type that sustained the most wide spread damage was with unreinforced masonry structures. Only a few of these structures were retrofitted and those that were have shown to have improved performance than those that were not. Reports indicate that there was a significant amount of nonstructural damage widespread over all building types, including elements such as glass and storage racks. Figure 2: collapsed masonry wall. Source: Martin Luff via Wikimedia Commons. Unreinforced Masonry Structures Early construction in New Zealand consisted of unreinforced masonry (URM) as the primary building method. It is estimated that around 900 URM buildings are located within the Canterbury region.

A sample of 595 URM buildings investigated showed that approximately 21% of these were determined to be unsafe to occupy (EERI 2010). The main modes of failure typically seen involve out-of-plane facade wall failures, parapet failures, chimney failures, and some in-plane damage. The lack of anchorage and reinforcement was the cause for number collapses of chimneys and gable end walls. An example of such failures can be seen in Figure 2, where a portion of the masonry wall and parapet had collapsed onto the adjacent sidewalk. Poor mortar quality also contributed to these collapses causing weathering in the mortar joints. Building construction between 1880 and 1930 utilized a lime mortar bond. Lime mortar is more susceptible to water ingress due to its porosity allowing for weakened strength between masonry units (Dizhur, 2010). Figure 3: St. John's Hororata Church. Source: Joel Wiramu Pauling via Wikimedia Commons. Churches are an example of structures typically designed using unreinforced masonry. St. John's Hororata Church was constructed in the early 1900's using stone masonry.

Effects of the earthquake caused the bell tower to collapse (see Figure 3) causing additional damage to the nave (Anagnostopoulou, 2010). Through a goverment effort to improve public safety, retrofitting of URM buildings had been voluntarily encouraged in recent years. URM buildings which had been retrofitted performed better and suffered far less damage than similar unretrofitted structures. Some of the retrofitting techniques include the application of through bolts or adhesive anchors, grout injections, addition of steel moment or braced frames, concrete moment frames and walls, and external steel rods, angles, and plates (EERI, 2010). Reinforced Concrete Structures (Pre-1970) Reports have indicated pre-1970 reinforced concrete buildings suffered only minor damages. The main failure modes typically observed include cracking to masonry infill walls, column hinging, and joint shear failures. Generally taller structures suffered more structural damage than one or two story buildings. This is mainly attributed in part to the flexibility of the structure and that taller buildings exhibit greater roof displacements. Stiffening elements such as masonry infill walls have shown to prevent significant structural damages.

Due to strong ground movement in the North South direction as a result of the earthquake, more structural failures were found to occur in those elements along the North South direction (Pampanin, 2010). Residential Structures Figure 4: underground manhole uplifted. Source: Jim Harding via Wikimedia Commons. Typical residential construction in New Zealand consists of light timber framing on a concrete slab or piled foundations. Residential buildings constructed within the last 20 year have concrete slabs. These are generally 4 inches in depth and have either limited or no reinforcement. Older residences primarily use timber or concrete piles with either reinforced or unreinforced concrete perimeter foundations. Exterior walls are built with traditional wood siding, stucco, or unreinforced brick veneer. The majority of damage caused by the earthquake to residential buildings was due to soil liquefaction. Soil liquefaction resulted in the damage to a large portion of residential buildings. Repairs to these residences is difficult if not impossible due to poor soil conditions. Geotechnical engineers must perform an individual analysis for each building to determine the appropriate course of action. Observations showed that structures built on piled foundations did perform better than those with concrete slabs.

This can be attributed to the piled foundations ability to allow for more differential settlement than concrete slabs. The addition of reinforcement to concrete slabs or increased thicknesses could have reduced structural damage to floor slabs. Settlement issues led to additional damages to windows, doors, and other non-structural elements. Chimney collapses were common in many residential buildings, often falling and damaging other areas (Buchanan, 2010). Steel Structures Overall, steel structures in the Canterbury area suffered minor damages. Preliminary reports showed that only minor inelastic behavior and plastic hinging started to occur within a week of the main event. Steel members exhibiting inelastic behavior were not in direct need of repair. Replacement was advised for some high strength connection bolts where connection slipping had occurred only for cautionary purposes. In cases involving combined steel and concrete lateral systems, damage had occured in some of the concrete elements. An example of this is a hospital parking garage which utilized eccentrically braced frames (EBF) consisting of concrete columns in conjunction with steel beams and bracing (see Figure 4). The concrete columns that supported a ramp built on the top story suffered damage due to shear failure.

Additionally, a few of the steel plates used in the EBF links demonstrated lateral-torsional buckling until being restrained. (Bruneau, 2010). New Zealand Building Code The New Zealand Building Code has been updated to account for the 2010 Canterbury earthquake. Many of these ammendments are based on the majority of damages assessed. Modification were made specifically to sections mentioning concrete, drains, glazing, and chimneys. Clauses of the concrete section were changed to include applications "to external walls which could collapse inwards or outwards from a building as a result of internal fire exposure," not just "outwards" as originally stated in the clause. Changes were also made to the minimum area of shear reinforcement for concrete elements. Additional reference documents were added the section on drains. These documents include "Methods of testing soils for civil engineering purposes," and the "New Zealand Geomechanics Society Guidelines" (Department of Building and Housing, 2011). As a result of a large number of glazing failures, ammendments were made to improve public safety from broken glass.

The use of glazing "within 2000 mm horizontally or vertically, from any part of a stairway or landing shall be Grade A safety glass." Glazing shall also meet certain barrier requirements when at a location 1000 mm or more above floor level. Due to the number of collapsed chimneys, the code amended that reinforcing steel used in chimneys shall conform to AS/NZS 4671. Brick chimneys shall be restrained using closed stirrups in the stack and "U" shaped bars elsewhere. Vertical reinforcing should also be use at all corners of the chimney. Forces due to liquefaction and lateral spreading on foundations were a large concern after the earthquake. Ammendments were made to the lateral strength of "free head" piles in cohesive soil, which have no restriction against head rotation when lateral displacement occurs (Department of Building and Housing, 2011). Although revisions were made to the structural building code as a result of the Canterbury earthquake, other modifications will need to be made to account for future information and events such as the 2011 Christchurch earthquake .

Similar Events On February 22, 2011 at 12:51 PM local time, a earthquake with a magnitude of 6.3 hit the city of Christchurch, NZ. The epicenter was closer to the populated city of Christchurch than the 2010 Darfield earthquake was. Figure 5 shows the locations of the epicenters and aftershocks of both the 2010 Canterbury earthquake and the 2011 Christchurch earthquake . The time of the event and the close proximity to the city attributed to the deaths of 184 people. The total damage had been estimated to cost $15 billion in repairs. Liquefaction was widespread, similar to the September 2010 event, affecting more than 50% of the Christchurch area. As a result, extensive damage was done to water lines, roads and highways, and electrical power lines. Approximately two to three times the number of unreinforced masonry structures were damaged than in the 2010 Canterbury earthquake. One explanation is that buildings which passed inspection during the September earthquake, were weakened enough to partially collapse during the February event.

Overall, the New Zealand Building Code will require updated requirements for seismic performance of all building types to prevent a similar occurance (EERI, 2011). Figure 5: comparison of the epicenters of the 2010 and 2011 events. Source: GNS Science. Lessons Learned As a result of improved building codes over the last few decades, many newer structures were left relatively undamaged. About 15 years prior, improvements were made to minimize the impact of natural disasters to infrastructure and other lifeline facilities. There are three major areas of concern for structures within the Canterbury region. Due to the regions composition of soft soils and sand, serious structural damage was caused by liquefaction of soil and lateral spreading. There was also considerable amounts of damage caused specifically to non-retrofitted URM buildings, many of which are historic structures. Lastly, there was widespread damage to non-structural building components, specifically glazing systems. Previous laws established in 1968, proclaimed local governments establish policies for buildings which are "earthquake prone." Due to the region being considered a moderate seismic zone, the local government enacted retrofitting policies only after major events.

After the both the 2010 and 2011 seismic events, the government now requires retrofits to be made within the next 30 years (EERI 2010). Conclusion The 2010 Canterbury earthquake hit the Canterbury region in the early morning on September 4th, 2010, registering a magnitude of 7.1. Liquefaction played an important part in causing major damage to both structures and infrastructure. Operation of underground utilities were disrupted as a result of increased soil pressures, causing manholes to lift out of the surface. Structurally, unreinforced masonry structures did not perform as well as other building types for a number of reasons. The lack of anchorage for masonry and poor mortar quality resulted in the collapse of numerous facades. As a result of modern building codes, minimal damage had affected newly constructed buildings. Investigations into the predominant failure types will help to further improve the New Zealand building code, in efforts to prevent a more catastrophic event. Bibliography Anagnostopoulou, Myrto et al.

"Performance of Churches During the Darfield Earthquake of September 4, 2010." Bulletin of the New Zealand Society for Earthquake Engineering 43, no. 4 (December 2010): 374-81. ~bruneau/NZSEE%202010%20Anagnostopoulou%20Bruneau%20Gavin.pdf Report: Investigation identifying the nature and cause of land damage associated with residential property through the liquefaction of soils. Bruneau, Michel et al."Preliminary Report on Steel Building Damage From the Darfield Earthquake of September 4, 2010." Bulletin of the New Zealand Society for Earthquake Engineering 43, no. 4 (December 2010): 351-59. ~bruneau/NZSEE%202010%20Bruneau%20Anagnostopoulou%20MacRae%20Clifton%20Fussell.pdf Report: Focusing on the seismic effects caused by the Darfield earthquake with respect to various steel structures including both concentrically and eccentrically braced frames.

Buchanan, Andrew and Newcombe, Michael. "Performance of Residential Houses in the Darfield (Canterbury) Earthquake (M7.1) 4th September 2010." Bulletin of the New Zealand Society for Earthquake Engineering 43, no. 4 (December 2010): 387-92. Report: Presenting observations and findings into the resulting damages experienced by residential buildings traditionally consisting of light timber framing. Department of Building and Housing. "Compliance Document for New Zealand Building Code Clause 1 Structure". New Zealand Government. Wellington, NZ. 2011: 88 Code: New Zealand goverment document listing ammendments made effective after August 2011 for seismic design of structural systems. EERI. "The Mw 6.3 Christchurch, New Zealand Earthquake of February 22, 2011." EERI Special Earthquake Report (May 2011): 16. Report: Providing a general overview of the events of the 2011 Christchurch earthquake and the structural damage various structures. EERI.

"The Mw 7.1 Darfield (Canterbury), New Zealand Earthquake of September 4, 2010." EERI Special Earthquake Report (November 2010): 12. Report: Providing a general overview of the geotechnical effects on the port of Christchurch and engeered structures along with the response and recovery to the aftermath. Dizhur, Dmytro et al."Performance of Unreinforced and Retrofitted Masonry Buildings During the 2010 Darfield Earthquake." Bulletin of the New Zealand Society for Earthquake Engineering 43, no. 4 (December 2010): 321-39. Report: Presenting selected case studies into the damages experienced with unreinforced masonry structures. Results are similarly compared with damages experienced with structures which have been retrofitted using various techniques. Pampanin, Stefano et al.

"Considerations on the Seismic Performance of Pre-1970s RC Buildings in the Christchurch CBD During the 4th Sept 2010 Canterbury Earthquake: Was That Really a Big One?" Presentation at the Ninth Pacific Conference on Earthquake Engineering Building an Earthquake-Resilient Society. Auckland, New Zealand. April 14-16, 2011. Presentation: Detailing the performance of reinforced concrete structures for those constructed prior to 1970. Tonkin & Taylor Ltd. (October 2010). "Darfield Earthquake 4 September 2010 Geotechnical Land Damage Assessment & Reinstatement Report." Tonkin & Taylor Investigation Report. September 30, 2010. 2010 Darfield Earthquake | 2010 Darfield Earthquake Submitted by Hamish Campbell on 18 October 2010 - 10:30 AM The Darfield Earthquake struck at 4:36 am on Saturday 4 September 2010.

It was magnitude 7.1, and since then GeoNet, the natural hazards surveillance arm of GNS Science, has recorded more than 1200 aftershocks. As anticipated, they are slowly diminishing in frequency and size with time. I neither felt the earthquake nor was woken by it here in Ngaio, Wellington. I do remember hearing the phone ring at about 7:00am but chose to ignore it and dozed off to sleep again. Some hours later, I determined that the call was from The Kim Hill Show at Radio NZ. In due course I responded and suggested to the producer that they had best contact my colleague Warwick Smith at GeoNet, which they did. Through the day I listened to the Radio NZ coverage of the event and its aftermath as the nature of the damage became known. The days have since stretched to weeks. In the week after the Darfield Earthquake, I was in Auckland attending the 11th International Engineering Geology Association congress at Sky City. There were 700 delegates including, as luck would have it, many of the world’s leading earthquake engineers. They were champing at the bit to visit Christchurch and see things for themselves.

I have no doubts that some people in Wellington were woken by the earthquake. I have friends in Paraparaumu who were woken by a large family dog that leapt on to their bed at exactly 4:36am. My mother was woken in Dunedin as was my brother and his family. Not to mention my many relatives and friends living in Canterbury! So what happened? Research by seismologists at GNS Science thus far indicates a complex event involving both compressional (thrust) and shear (strike-slip) motion. The strong motion records for the earthquake show two major pulses of strong shaking separated by the order of 5-10 seconds. A 29km long, roughly east-striking fault break was produced by the earthquake, where active faults have previously not been mapped. The surface expression of the new fault has been named the Greendale Fault. The northern side of the fault was moved about 4 metres to the east relative to the southern side. The main earthquake epicentre (the point on the earth’s surface projected vertically above the hypocentre) was located some 40 kilometres west of Christchurch near Darfield, hence the name of this event.

The hypocentre (the actual point source of the earthquake at depth within the earth, where the earthquake rupture process began) was located some 10 kilometres below the surface. The Greendale Fault ruptured between Greendale and Rolleston, offsetting numerous linear features in the rural, flat, farmed landscape of the Canterbury Plains, including streams, irrigation channels, ditches, drains, hedges, fences, tracks and roads. The numerous aftershocks relate to adjustment and “settling down” of the fault, and extend beyond the observable surface rupture. Some small events on other faults in the general region may have been triggered by the Darfield event. While the magnitude and rare occurrence of the Darfield earthquake was already anticipated in both nationally-based and Canterbury-based seismic hazard calculations for the region, the exact timing and geometry of the event and causative fault was not. The occurrence of the event will focus our efforts on trying to improve seismic hazard models to better forecast events for (e.g.) the time span of a human lifetime.

Given that the Darfield earthquake ruptured the ancient (16,000 year old) surface of the Canterbury Plains for the first time in the area, the recurrence interval of the causative Greendale Fault must be measurable in the tens of thousands of years. In response to the Darfield Earthquake, scientists from GNS Science and various universities have been mobilised for a variety of research activities and in particular the recording and mapping of surface deformation phenomena. Many instruments (mainly seismometers and GPS instruments) and methodologies have been deployed and in time a great deal of new data and research will result in a better understanding of what happened. It is early days as yet. We shall have to wait and see what satellite radar interferometry studies have to offer in terms of how the surface of Canterbury has changed shape, along with detailed seismology and GPS studies. My GNS Science colleagues have traversed the total length of the Greendale Fault rupture on foot, measuring offset linear features and en echelon geomorphic features developed along its length. These include many broad welts, ridges and fissures along the trace of the fault.

They are substantive, producing a relief involving uplift and subsidence of at least 3 metres and deformation of a surface (dominated by river and glacial outwash gravels) that has been subject to minimal deformation and/or erosion processes for 16,000 years. Such geomorphic features have not been recognised previously in this part of the Canterbury Plains. They are fragile features, and will be largely gone from the landscape with ongoing land use in the area (e.g. ploughing). In terms of plate motion and plate collision, which is the underlying ‘awesome force’ responsible for the Darfield Earthquake, this event was ‘business as usual’. It was the result of pent-up accumulated strain within the earth’s crust as a result of the collision between the westward moving Pacific Plate and the northward moving Australian Plate. The actual plate boundary, the Alpine Fault, lies some 90 kilometres west of Christchurch, so Christchurch and most of Canterbury are located on the Pacific Plate. The rate of collision is well-established from direct measurement and is 4 to 5 centimetres per year.

Research suggests that some 80% of this motion is accommodated by movement on the actual plate boundary, and that the remaining 20% of deformation is taken up on faults distributed within a broad zone of Canterbury up to 100 kilometres east of the Alpine Fault. The Darfield Earthquake may therefore be interpreted as part and parcel of this 20% ‘relief effort’. The east-west orientation of the Greendale Fault rupture came as a surprise to most earth scientists. This is because the main ‘structural grain’ of New Zealand is NE-SW, which is the sum vector orientation one might expect between two entities (the plates) moving in different directions (one to the west, the other to the north). Furthermore, most active faults associated with plate collision are oriented NE-SW. However, if we consider Canterbury as just an on-land western end of the Chatham Rise, we get a clearer picture.

If we ‘remove’ Banks Peninsula (an intra-plate basalt volcanic complex that erupted between 10 and 6 million years ago), and the young gravels (less than 2 million years old) of the Canterbury Plains, what we would see is geology compatible with that of the Chatham Rise, including major east-west oriented faults. Oil company exploration of the Chatham Rise in the 1970s produced a great deal of very useful data that were subsequently summarised and published by GNS Science in the early 1990s. Our knowledge of the geology of the Chatham Rise is largely based on this work but it is also well-supported by our knowledge of the geology of the Chatham Islands. Indeed, the east-west prolongation of northern Chatham Island is controlled by major east-west trending normal faults. ‘Normal’ faults involve elongation of the earth’s surface as a function of stretching, whereby one side of the fault slides down the other. This is the opposite of a thrust or ‘reverse’ fault which is associated with a net shortening of the earth’s surface. These old normal faults relate to stretching of the crust when Zealandia was rifted away from Gondwanaland.

This ‘stretching’ phase of our geological history lasted for about 100 million years but has been reversed i.e. subject to compression or collision, for the past 23 million years. It is thought that the Greendale Fault is most probably one of these old Zealandian normal faults that have been reactivated. However, it may not be! A common question about large earthquakes is this: how do you know that it isn’t just a precursor to something even bigger? The simple answer is that we don’t, at least not initially. However, things improve greatly as time passes. Some statistical studies give probabilities of a larger earthquake occurring soon after the original large earthquake, and in a close-by location. If nothing happens though, we can be more confident that things are settling down. This knowledge is based on almost 100 years of sustained global research effort on patterns of seismicity associated with large earthquakes. Christchurch and Canterbury had good planning and good luck on their side. It is nothing short of miraculous that no one was killed.

To put things in stark perspective, the magnitude 6.5 Boxing Day 2003 Bam Earthquake in southern Iran involved rupture on a blind fault, not unlike the Greendale Fault, and 50,000 people were killed. The more similar 7.0 Haiti Earthquake on 12 January this year killed 200,000 people. Everyone in Canterbury, if not the whole of the South Island, but especially those in Christchurch, will have their own story to tell of the Darfield Earthquake. I came across two very different versions last weekend which are worthy of mention. I was on my way to an event at the Te Hikoi Southern Journey Heritage Museum in Riverton which involved driving from Dunedin. I picked up a hitch-hiker just south of Gore. (It was snowing at the time). He told me that he was ‘fleeing from Christchurch’ and that he was ‘terrified by earthquakes’. He had lost all his possessions which he had had in storage in a friend’s brick garage. The brick walls had collapsed and crushed his possessions and then if that were not enough, everything was ruined by water damage resulting from liquefaction-related effects.

He was on his way to his mother in Invercargill and was clearly traumatised. He had been with his sister in Methven since the main earthquake. I eventually arrived in Riverton after dropping the hitch-hiker off at his mother’s house and was met by a lady at Reception at Te Hikoi. She was simply raving about the Darfield Earthquake. To her it had been the most wonderful experience and she felt very privileged to have been in Leeston at the time to feel it all. All care and no responsibility perhaps but oh what joy she expressed! Each to their own… The Darfield Earthquake is the most damaging earthquake to strike New Zealand since the 1931 Hawkes Bay Earthquake that so badly affected Napier, Hastings and Wairoa with more than 250 deaths. The Darfield Earthquake was notable in two other respects: as measured by strong motion instruments, it generated the highest recorded ground accelerations (1.25 times that of gravity) ever recorded from New Zealand, and it also generated a great deal of liquefaction.

In many respects the Darfield Earthquake was similar to the Inangahua Earthquake of 1968: it too measured 7.1, the hypocentre was 10 kilometres deep, there was very strong ground acceleration and considerable liquefaction; furthermore it was complex, perhaps involving movement on more than one fault plane. Interesting! Previous earthquakes that have adversely affected Christchurch include the following: 1869, June 5: Magnitude less then 6 "Christchurch" earthquake 1870, August 31: less than 5 "Lake Ellesmere" earthquake 1888, September 1: 7.1 "North Canterbury” (Hope Fault) 1929, March 9: 7.1 "Arthur's Pass“ …and more recently: Earthquake of 7.1 magnitude hits New Zealand city Earthquake of 7.1 magnitude hits New Zealand city (Agencies) Large Medium Small WELLINGTON - A major earthquake hit New Zealand's second biggest city Christchurch early on Saturday, bringing down power lines, ripping up roads and wrecking building facades, but authorities reported no deaths.

Authorities declared a formal civil defence state of emergency to coordinate recovery operations in the city, which has a population of about 350,000 people, after facades collapsed into streets, crushing cars and blocking roads. A partially wrecked van is seen in this video frame grab near Christchurch, New Zealand, September 4, 2010. [Photo/Agencies] Two men suffered serious injuries and police closed off the central business district. The earthquake had a magnitude of 7.1 and a depth of 10 kms (6 miles), hitting the South Island city and a large surrounding area of farms at around 4.35 a.m. local time (1635 GMT Friday). Related readings: 6.3 magnitude earthquake hits Papua New Guinea "There's a lot of damage that I've been able to observe in the central city area, mainly of the old brick and masonry buildings, a number of those have got walls that have fallen into the street," Christchurch mayor Bob Parker told Radio New Zealand. The city's hospital said two men had been admitted with serious injuries, one hit by a falling chimney and the other cut by glass.

It had also treated a few other people with broken bones, cuts and grazes. Police said there were several instances of looting, which had been quickly contained. In the suburbs many houses had broken windows, toppled chimneys, cracked walls and items thrown off shelves. Power was out over a large area of the city and surrounding region as circuit breakers were tripped at substations, but was being progressively restored after safety checks. Water and sewage services were also disrupted, and there were reports of subsidence in some roads. Rural epicenter Officials were checking how severe the damage was in rural areas, closer to the epicentre, west of the city. Ray O'Donnell, owner of a hotel in Darfield, a small farming community around 20 kms (12 miles) west of Christchurch, said large cracks had appeared in rural roads near the epicentre. GNS Science, the New Zealand government seismological agency, revised its reading of the quake to magnitude 7.1 from an original 7.4. The US Geological Survey initially reported it at 7.4 but later revised its figure to 7.0.

The city's airport was shut as the runway and facilities were checked, and the railway network and bridges throughout the region were also being checked for damage. The quake was felt as a long rolling motion lasting up to 40 seconds. The area was continuing to feel aftershocks as strong as magnitude 5.2. "It was a real rocker, and (we're) still getting aftershocks. (It) felt like the house was flying on a whirlwind," Tessa Hay, who lives around 12 km north of the city, told Reuters. Because the quake occurred inland there was no danger of a tsunami. "No destructive widespread tsunami threat exists based on historical earthquake and tsunami data," the Pacific Tsunami Warning Centre said. New Zealand scientists record around 14,000 earthquakes a year, of which around 20 top magnitude 5.0. The last fatal earthquake in the geologically active country, caught between the Pacific and Indo-Australian tectonic plates, was in 1968 when an earthquake measuring 7.1 killed three people on the South Island's West Coast. A car is seen under debris after a major earthquake in Chirstchurch, New Zealand, September 4, 2010.

[Photo/Agencies] Christchurch Rebuild Tour | Exploring my own backyard Exploring my own backyard Kiwi lad exploring his home country New Zealand Widgets Christchurch Rebuild Tour , is a guided bus tour of Christchurch city’s progress to rebuild following the earthquakes in 2010 and 2011. Site of recently demolished police station At 4:35 am on Saturday 4th September 2010 a 7.1 magnitude earthquake struck the Canterbury region. The epicentre of the quake was located 40 kilometres (25 miles) west of Christchurch, near Darfield. The earthquake caused power cuts and widespread damage particularly to Christchurch. There were no deaths as a result of the earthquake, but one person died of a heart attack. Tragically on Tuesday 22 February 2011 at 12:51 pm a 6.3 earthquake struck. This quake was centred 2 kilometres (1.2 miles) west of Lyttelton and 10 kilometres (6 miles) south-east of Christchurch city centre. 185 people from more than 20 countries were killed, making it the second deadliest natural disaster in New Zealand history.

The tour, which departs from outside the Canterbury Museum (Rolleston Ave) daily at 11:00 am, lasts approximately 90 minutes. There is a driver and onboard guide from the Canterbury Museum that does an informative commentary accompanied by video and photographs. Tickets can be purchased online , by phone (0800 500 929) or from the i-SITE Visitor Centre, next to the Museum. No tour is exactly the same as where the bus travels depends on traffic conditions and works that do. The bus may make stops were passengers can disembark with the guide. The Rebuild Tour bus Our tour made two stops. The first stop was at the site of the Cathedral of the Blessed Sacrament. It was the mother church of the Roman Catholic Diocese of Christchurch. The buildings were designed by architect Francis Petre and completed in 1905. The Cathedral closed following the September earthquake. The parish moved St Mary’s Pro Cathedral (373 Manchester Street). During the February earthquake the two bells towers at the front of the building collapsed along with much of the front façade. The dome, which had received major cracking was later removed, and the rear of the Cathedral was demolished.

Also during the February quake the statue of Virgin Mary located in the north tower rotated 180 degrees to look out the window. The statue became a symbol of survival following quake. In May this year it was announced the diocese has plans to attempt to preserve the nave as part of a rebuild. Cathedral of the Blessed Sacrament The next stop was at the 185 Empty White Chairs installation on the site of the former St Paul’s Trinity Pacific Presbyterian Church on the corner of Madras and Cashel streets. The memorial designed by artist Pete Majendie was previously located on the site of the former Oxford Terrace Baptist Church. Each white painted chair represents one of the lives lost in the 2011 Christchurch earthquake. The installation sits on 185 square metres of ready made lawn. 185 White Empty Chairs Magnitude 6.3 Earthquake near Christchurch, NZ : Image of the Day News & Notes acquired September 3, 2010 - February 22, 2011 download large image (374 KB, JPEG, 1198x1198) At 12:51 p.m.

local time on February 22, 2011 (11:51 p.m. February 21 UTC), a 6.3-magnitude earthquake struck the South Island of New Zealand, the U.S. Geological Survey (USGS) reported. Several smaller aftershocks followed. The quake occurred near the city of Christchurch, a community of some 400,000 residents on the east coast. The initial death toll was 65, according to news reports, and authorities warned that the toll could rise sharply as search-and-rescue efforts continued. This map shows the earthquakes that occurred near Christchurch since September 3, 2010. On that day a magnitude 7.1 quake struck to the west of Christchurch. Black circles represent earthquakes from September 3, 2010, until February 21, 2011. Red circles show the locations of the magnitude 6.3 quake and aftershocks on February 22 and the morning of February 23. Larger circles represent stronger earthquakes. Yellow shows urban areas, including Christchurch.

The USGS characterized the 6.3-magnitude quake on February 22 as an aftershock of the quake that struck to the west, in Darfield, New Zealand, on September 3, 2010. Darfield lies about 50 kilometers (30 miles) west-northwest of Christchurch. Although no specific tectonic structure linked the two events, numerous aftershocks of the September quake occurred along a roughly east-west line, as this image indicates. The USGS stated that the quakes were associated with regional tectonic plate boundary deformation. The Pacific Plate and the Australia Plate interact under the South Island of New Zealand. The Darfield earthquake in September 2010 caused no casualties, even though it had a higher magnitude. Besides striking closer to a major population center, the 6.3-magnitude Christchurch earthquake had a depth of just 5 kilometers (3 miles). The New Zealand Herald reported that, whereas the Darfield quake happened in the early morning hours, the February 22 quake struck at the “worst possible time” of day—at the lunch hour when city streets were crowded with shoppers, diners, office workers, and school children.

Moreover, some of the buildings that collapsed may have been weakened by the September 2010 quake. Effects of the Christchurch earthquake were felt some 200 kilometers (125 miles) away, along the South Island’s west coast. A 30 million-tonne (33 million-ton) chunk of ice broke off from the Tasman Glacier, and slid into Tasman Lake. In fact, officials had expected ice would break off the glacier, although they expected the event to result from heavy rainfall caused by La Niña. References New Zealand earthquake moves Earth's surface '11ft to the right' | Daily Mail Online Enlarge Destruction: A man walks over a damaged road in Paiapoi, 13 miles south of Christchurch after the city was hit by an earthquake Saturday The quake was caused by the continuing collision between the Pacific and Australian tectonic plates, said Professor Mark Quigley, of Canterbury University. ‘One side of the Earth has lurched to the right ... up to 11ft and in some places been thrust up,’ he said.

‘We went and saw two houses that were completely snapped in half by the earthquake.’ The quake cut power across the region, roads were blocked by debris and gas and water supplies were disrupted. Christchurch mayor Bob Parker said power was back to 90 per cent of the city and water supply had resumed for all but 15 to 20 per cent of residents. This US Geological Survey (USGS) shows on image of a ShakeMap of the South Island of New Zealand on Friday as an earthquake with a magnitude of 7.2 on the Richter scale struck Enlarge A seismogram made available by Geosciences Australia of the early morning earthquake which hit west of the southern city of Christchurch Portable toilets had been provided and tanks of fresh water placed around the city. Mr Parker said it would take a long time to fix fully some core services such as water and sewerage. ‘Our first priority is just people,’ he said. ‘That’s our worry.’ The fact that no one was killed was put down to the timing of the quake and strict building codes.

RELATED ARTICLES Enlarge A man on a pushbike (R) photographs a damaged building in New Zealand's second largest city Christchurch The Anglican Dean of Christchurch, the Rev Peter Beck, added: ‘Thank God for earthquake strengthening ten years ago.’ Prime Minister John Key said it was a miracle no one was killed. He put that down to the building codes and because the quake happened just before dawn on Saturday. ‘If this had happened five hours earlier or five hours later there would have been absolute carnage in terms of human life,’ he said. Parts of the city look like they’ve been put in the tumble dryer.’ Up to 90 extra police officers had flown in to Christchurch to help and troops were likely to join the recovery effort today. Engineering teams have begun assessing damage to all central areas. Enlarge Rebuilding infrastructure such as roads, water and sewerage systems 'would be a major cost' that the government would have to meet Schools across the region will remain closed for the next two days to allow time to check whether they were safe.

Roger Bates, whose dairy farm at Darfield was close to the quake’s epicentre 19 miles west of Christchurch, said the new faultline had ripped up the surface across his land.‘The whole dairy farm is like the sea now, with real soil waves right across the dairy farm. ‘We don’t have physical holes (but) where the fault goes through it’s been raised a metre or metre and a half.’ New Zealand records more than 14,000 earthquakes a year, but only about 150 are felt by residents. Fewer than ten a year do any damage.

Question: The epicentre of an earthquake in September last year (2010) was at Darfield, 25 miles west of which city in New Zealand?
Answer: CHRISTCHURCH